This invention relates to a mine roof support unit, and to a longwall mineral mining installation incorporating mine roof support units.
A longwall mineral mining installation typically comprises a longwall conveyor, a winning machine movable to and fro along the longwall face, and a plurality of roof support units for supporting the roof of the working. Each of the roof support units has a roof bar supported on a floor sill by hydraulic props. When such an installation is used for winning coal, the roof support units are usually positioned on the goaf side of the conveyor, and a winning machine (such as a plough) is movable to and fro along the face side of the conveyor. In order to support the roof of the longwall working in the region adjacent to the face, the roof bars are provided with extension caps. These extension caps are pivotally or slidably mounted on their respective roof bars. Unfortunately, the load-bearing capacity of such an extension cap is relatively small, and is often insufficient to provide effective roof support when depressions or cracks occur in this critical roof zone adjacent to the face.
In order to improve the load-bearing capacity of mine roof support units in the region adjacent to the face, it is known to support the roof bars by means of hydraulic props positioned immediately in front of the face. With this arrangement, the roof can be supported reliably, even under difficult conditions. (See DE-PS No. 1 143 721, DE-AS No. 1 583 083 & DE-AS No. 1 205 031).
A known installation incorporating roof support units of this type is provided with advance mechanisms for advancing the roof support units. The roof support units of each adjacent pair are interconnected by means of a respective advance mechanism, each advance mechanism being used to advance its two associated roof support units in turn. In this case, the conveyor is carried by the floor sills of the roof support units, and is positioned between the face-side props and a row of props positioned at the goaf side of the roof support units. (See DE-Gbm No. 1 886 508).
The disadvantage of this known type of installation is that the distance through which the roof support units can be advanced is relatively small. The advance distance is considerably less than the distance between the face-side props and the goaf-side props. Consequently, the width of the working (that is to say the distance between the face and the goaf) is relatively large.
The aim of the invention is to provide a roof support unit that can reliably support the roof in the region adjacent to the face, and which can be advanced by a relatively large distance without the need for an excessively wide working.